Office chairs have been developed where seat and back assemblies thereof are tiltable forwardly and rearwardly. One type of office chair is commonly referred to as a "synchro-tilt" type chair wherein the back assembly tilts synchronously with respect to the seat assembly but at a greater rate. While numerous improvements to these chairs have been made to improve the comfort of a user, for example, with respect to the design of the seat and back assemblies, such office chairs typically includes planar sheetlike inner shells which support the seat and back of a user. These inner shells typically are directly supported on a bottom surface thereof by rigid structures such as a housing for a tilt control mechanism or a vertical upright which supports the back assembly. Since these inner shells are typically formed of plywood or of thick or reinforced plastic sheets and are directly supported generally in the central regions thereof where the seat and back of a user typically are positioned, seat and back cushions are provided in an effort to provide comfortable and ergonomic support of a user. While the cushions conform to the contours of the user, these cushions are still typically supported by relatively rigid shells. Thus, when the cushions are highly compacted by the weight of a user, the seat and back assembles often provide a greater degree of rigidity than is desired.
To assist in accommodating the contours of a user, the relatively rigid inner shells typically are curved and contoured in an effort to increase the comfort of the user. Since each user has their own individual characteristics, such contours as provided to the inner shells are determined according to the characteristics of an "average" user. However, since each occupant has unique characteristics with respect to body size, contour and shape, an occupant still may not necessarily conform to the contour of the inner shell. Further, the contours of the inner shell tends to accommodate a user when stationary, and thus the contoured shapes do not necessarily accommodate user movements such as twisting or shifting.
In an effort to provide greater comfort, chairs have been provided which attempt to accommodate the individual characteristics of the user, as well as movements thereof, by providing flexible support surfaces for the seat and back. For example, one office chair provides a suspended sheet of material which is similar to a woven plastic material that is supported on its edges and thereby attempts to conform to the characteristics and movements of a user. This material is exposed during use so as to depart from the conventional appearance of an office-type chair which typically uses cushions.
In other office-type chairs, the seat and/or back are defined by sheetlike elastic materials which are formed into elongate spring elements which anchor at opposite ends on opposite side frame elements, and the intermediate spring is defined by a closely positioned sinusoidal configuration, with the spring typically having significant width for direct contact with the posterior or back of the occupant. With such arrangement, one or more such springs typically extend transversely of the seat or back, and are anchored solely at the ends, and provide for control of forces solely in a single transverse direction. Such arrangements thus often provide too much and uncontrolled flexibility, and in particular do not provide for desired uniform control of flexibility in both transverse directions of the seat or back.
In still another chair intended for use in an office, the seat and back areas are open and bungee cords are extended sidewardly from frame members on opposite sides of the chair. Here again, the seat and back are open and the suspension system is exposed during use.
Other examples are chairs of the type having a fixed nontiltable rigid frame formed of tubular members. These chairs use an exposed open webbing formed of plastic-coated spring wires which are connected along the opposite side edges thereof to the fixed frame and support the seat and back of a user in the open areas between the frame members. These chairs, however, individually connect the spring wires to the side frame elements, and do not provide uniformity in the transverse supporting directions of the seat and back.
Examples of chairs of the type described above are illustrated by U.S. Pat. Nos. 2,649,146, 3,720,568, 3,767,261, 4,202,581, 4,390,204, 4,502,731, 4,533,174 and 4,660,887.
In view of the foregoing, it is an object of the invention to provide an improved office-type chair provided with cushions for the seat and back which are supported by a dynamic suspension system to accommodate the contours and movements of a user. It is a further object that this suspension system include plastic inner membranes which support the cushions over an entire interior surface thereof while being at least of limited resilient flexibility at least in the center region thereof. It is a still further object to provide a chair frame which supports the inner shells on the peripheral edge thereof so as to support the seat of a user bi-directionally, i.e. both sidewardly between the opposite sides of the chair and rearwardly between the front and back of the chair. Similarly, it is an object to also support the back of a user bi-directionally, i.e. both sidewardly and vertically between the top and bottom of the chair back. It is a further object that the inner membranes be of a one-piece construction to which the cushions may be fixedly attached to define a cushion assembly.
More specifically, the present invention relates to an improved chair, particularly an office-type chair, having separate seat and back parts each being cushioned and employing a thin inner plastic shell having a central region formed generally as a thin membrane which is supported solely around the peripheral edge thereof by a suitable ringlike support frame. This membrane is relatively strong and generally semi-rigid in the plane thereof, but possesses at least limited resiliency or flexibility in the direction of the thickness thereof and, being free of direct underlying support, provides direct support for the cushion which in turn is engaged by either the back or posterior of the chair occupant to thus provide for limited flexibility while at the same time providing for desirable comfort and ergonomic support. The membrane in the central region is preferably provided with a first series of strips which extend between the border of the membrane, with the first strips extending transversely across the membrane in one direction in spaced relationship, and a second series of such strips extending transversely across the membrane in the other transverse direction. The individual strips of the two series intersect and are integrally joined so as to provide the central region of the membrane with a gridlike construction as defined by the strips. This gridlike construction, and the fact that the occupant loading is imposed transversely thereon due to the pressure of the back or posterior, transmits this transverse loading substantially uniformly radially outwardly to the surrounding border of the membrane, and thence to the appropriate supporting frame, to provide the desired resilient support of the occupant.
Other objects and purposes of the present invention, including the desired structural and functional aspects thereof, will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.